1. Field of the Invention
The present invention relates to indicators for use in spectrophotometric detection of chemical compounds. More particularly, the present invention relates to binding arsenazo III and other indicators to substrates for use in spectrophotometric analysis. The United States Government has fights in this invention pursuant to Contract No. DE-AC09-898R18035 between the U.S. Department of Energy and Westinghouse Savannah River Company.
2. Discussion of Background
The use of indicators to facilitate visual identification of chemical compounds is well known. An indicator is typically a substance that undergoes a noticeable change, chemical or otherwise, in the presence of another material. For example, an indicator may luminesce, absorb light energy or change colors in the presence of a particular material of interest. Examples of materials measured include oxygen, carbon dioxide, hydrogen ions (pH), electrolytes, and glucose. Obviously, the properties of indicators make them useful in various types of sensing instrumentation.
In the past, indicators were used by dissolving them in a solution containing the material of interest or by applying them as a coating onto paper that was then put into contact with a fluid sample. However, such conventional testing methods destroy the fluid sample and indicator paper, and thus are non-reusable and often costly.
One of the more recent uses of indicators is with optical sensing devices. Optical sensing devices are well known for measuring the presence and concentration of a chemical compound in a medium, such as a solvent. When used with optical sensors, an indicator, often in combination with a sample-permeable matrix, is positioned to interact with the sample in the medium, which is near or adjacent to a transmitting optical fiber. The interaction between the indicator and the chemical to be sensed or measured alters the light being transmitted prior to its receipt by a receiving fiber. The indicator may absorb, reflect, refract, scatter, fluoresce, or emit Raman radiation in altering the incident light. By comparing the received light to the transmitted light, the concentration of the chemical compound being detected can be easily determined.
Various techniques for immobilizing indicators on substrates for use by instrumentation in detecting chemical compounds are known. In one specific instance, L. T. Mimms et al., in their article titled "Spectrophotometric Study Of Coverage And Acid-Base Equilibrium Of A Chemically Bonded Base", Analytical Chemistry., Vol. 89, pgs. 355-361 (1977), describe the immobilization of an aniline azo dye on a glass slide by reacting an organosilane reagent with the surface of the glass slide. Also, in an earlier, related article titled "Reusable Glass-Bound pH Indicators", Analytical Chemistry, Vol. 47, pgs. 348-351 (February 1975), G. B. Harper describes a chemical system in which a variety of pH indicators are immobilized on porous glass materials for use in optical absorption spectrophotometric analysis. Glass-bound pH indicators offer several advantages over conventional indicator applications, including the capability of repeated use, resistance to microbial attack, and insolubility such that samples and systems are not contaminated.
Several sensors are known for use in detecting radiation from, for example, uranium. For instance, see U.S. Pat. No. 4,467,208, issued to Meiller et al., U.S. Pat. No. 4,198,568, issued to Robbins et al. and U.S. Pat. No. 4,158,769, issued to Smith.
Both Smith and Robbins et al. disclose methods for detecting uranium in solution. Robbins et al., illuminate a uranium-containing sample with ultraviolet light to cause uranium compounds to luminesce. Smith uses a series of filters to pass specific radiation through to a radiation counter.
There exists a need for indicators suitable for binding other compounds, including uranyl indicators, to substrates for spectrophotometric analysis.